The first-ever congressional hearing on the use of solitary confinement in US prisons has begun in Washington.

Members of the Senate judiciary subcommittee on the constitution, civil rights and human rights are hearing testimony from a range of speakers including a former prisoner who spent years locked alone in his cell for a murder he did not commit, a psychology professor who has studied the effects of long-term prison solitude, a senior prison official who has eschewed his support for the tactic, and a former Republican assemblyman who is at the forefront of the conservative movement for prison reform.

The hearing follows a year in which thousands of prisoners across the country took part in coordinated hunger strike in response to California’s extensive use of solitary confinement, and it comes less than one month after an unprecedented class action lawsuit challenged the constitutionality of holding hundreds of men in solitary for a decade or more at the state’s Pelican Bay facility.

Illinois Democrat Dick Durbin, chairman of the committee, issued a statement indicating the hearing will “focus on the human rights, fiscal and public safety consequences of solitary confinement in US prisons, jails and detention centers.”

“During the last several decades, the United States has witnessed an explosion in the use of solitary confinement for federal, state and local prisoners and detainees. The hearing will explore the psychological and psychiatric impact on inmates during and after their imprisonment, fiscal savings associated with reduced use of solitary housing units, the human rights issues surrounding the use of isolation, and successful state reforms in this area,” the statement said.

Prison reform advocates have welcomed the hearing, with supportive statements issued from a range of legal organizations, community groups and representatives of the faith community.

“It’s a tremendously significant development,” said David C Fathi, director of the American Civil Liberties Union national prison project.

While the hearing will cover the state of solitary confinement in the US and is not examining legislation proposals, Fahti said a number of steps can be taken to address the issue. While an estimated 25,000 prisoners are currently held in solitary confinement in the country and another 80,000 believed to be held in so-called restrictive housing, information on the scope of the punishment remains difficult to obtain.

“We just need greater oversight and reporting requirements about prisons and jails’ use of solitary. Right now there are none, and so getting a piece of information as basic as how many prisoners are in solitary on any given day is a very difficult undertaking,” Fahti said.

He added, however: “We already know enough to make some very concrete recommendations. First of all, people with mental illness are highly over-represented in solitary confinement.” He said an inability to manage the stresses, rules and expectations placed upon mentally ill prisoners in solitary confinement often results in their prolonged isolation.

“People with mental illness, if you put them in solitary confinement, most of them will break down quite dramatically,” he said. “More than half the jail suicides in this country occur in solitary confinement.”

Fahti said there should be a prohibition on placing mentally-ill prisoners in solitary confinement. “Same with children,” he added, noting that juveniles who are housed in adult prisons and jails are sensibly separated from the adult population, but as a result are sometimes kept in isolation.

Finally, Fahti added, there need to be “durational limits” on the amount of time prisoners can spend in solitary confinement.

“The US is an outlier, not only in how many people it puts in solitary, but in how long they stay there,” he said. The American Bar Association has recommended that prisoners not be held in solitary confinement for more than one year, while the United Nation’s expert on torture says isolation that lasts more than 15 days can amount to torture.

With just five percent of the global population and a quarter of the planet’s prisoners, Fahti says the United States is without equal in its use of solitary confinement when compared to other democratic nations.

“No other democratic country comes close to the US in its use of solitary confinement, both in terms of the number of people in solitary and the extraordinary lengths of time that many of them stay there,” Fahti said.

The witnesses at Tuesday’s hearing include Harley Lapin, director of the federal bureau of prisons, representatives from the US justice department, and corrections officials from Maryland and Illinois.

They will be joined by Anthony Graves, who in 1982, along with a man named Robert Carter, was convicted of killing a Texas woman, her daughter and her four grandchildren. Moments before his execution in 2000, Carter admitted Graves was not involved in the crime. Graves was eventually exonerated in 2010 after spending 18 years behind bars, the bulk of that time on death row and in solitary confinement.

University of California psychologist Craig Haney, one of the foremost experts on the impact of solitary confinement on the human brain will also address the committee. While testifying before the California assembly’s committee on public safety last year, Haney said that all of the men housed at Pelican Bay – and many more held in similar conditions at other facilities – were routinely treated “worse than prisoners in any civilized nation anywhere else in the world are treated, under conditions that many nations and international human organizations regard as torture.”

Haney said the men he interviewed at Pelican Bay “complain of chronic and overwhelming feelings of sadness, hopelessness and depression” adding that they were “paying a terrible price as pawns in this failed experiment”.

Mississippi’s commissioner of corrections, Christopher B Epps, has also been called to testify. In 2007, Epps was responsible for the state’s super-maximum security prison, a facility that was rapidly descending into chaos, where prisoners held alone for 23 hours a day in insect-infested cells – the walls smeared with excrement – listened to mentally ill men scream through the night. Tensions increased, leading to stabbings, murders and suicides.

Rather than crack down, prison officials relaxed the harsh conditions, allowing the men recreation, privileges and human contact. The number of prisoners held in isolation fell dramatically. Since that time Mississippi has become symbol of potential in solitary confinement reform. The perceived success in the state prompted Colorado, Illinois, Maine, Ohio and Washington state to begin the process of reducing the number of inmates held in long-term isolation. Epps, who once believed in locking men down as tightly as possible, now advocates for more humanitarian alternatives.

Former Republican leader of the California state assembly and current vice-president of Prison Fellowship, Pat Nolan, another witness in the hearing, has argued for reducing prison spending by cutting the “astronomical growth” in the prison population, which is expanding 13 times faster than the general population and cost taxpayers $68b in 2010.

“Solitary confinement is actually the most expensive form of incarceration, costing up to three times much as general prison population housing. Indeed, Mississippi has reportedly saved $5m by closing its super-max unit, and Colorado will save $4.5m as a result of its pending supermax closure,” Nolan wrote in recent letter he co-authored with the reverend Richard Kilmer, executive director of the National Religious Campaign Against Torture.

Alexis Agathocleous, an attorney with the Center for Constitutional Rights, one of the organizations involved in filing the class action lawsuit targeting Pelican Bay, supports the witnesses’ diverse relationships to the punishment.

“They come from a broad range of perspectives, and I think that what it will serve to illustrate is the range of concerns that the overuse of solitary confinement raises,” he said.

“We know that keeping someone in solitary confinement puts them at very serious risk of descending into irreversible mental illness,” he said. “That’s not tolerable in a society that values the dignity and humanity of all people, no matter whether they are incarcerated or not.”